Methods, systems and apparatus for detecting material defects in combustors of combustion turbine engines

ABSTRACT

A system for detecting defects in a combustion duct of a combustion system of a combustion turbine engine while the combustion turbine engine operates, wherein the combustion duct comprises a hot side, which is exposed to combustion gases and, opposing the hot side, a cold side. The system may include: an indicator coating disposed on an outer surface of the combustion duct, the indicator coating comprising a detectable substance; and a gas sensor positioned downstream of the combustor, the gas sensor configured to take a measurement of the amount of the detectable substance in the combustion products of the combustion turbine engine.

BACKGROUND OF THE INVENTION

This present application relates generally to methods, systems, andapparatus for detecting defects, including surface defects, which mayoccur in industrial manufacturing processes, engines, or similarsystems. More specifically, but not by way of limitation, the presentapplication relates to methods, systems, and apparatus pertaining to thedetection of defects that form on the components, such as those foundwithin the combustor, exposed to the hot-gases of combustion turbineengines.

In operation, generally, a combustion turbine engine may combust a fuelwith compressed air supplied by a compressor. As used herein and unlessspecifically stated otherwise, a combustion turbine engine is meant toinclude all types of turbine or rotary combustion engines, including gasturbine engines, aircraft engines, etc. The resulting flow of hot gases,which typically is referred to as the working fluid, is expanded throughthe turbine section of the engine. The interaction of the working fluidwith the rotor blades of the turbine section induces rotation in theturbine shaft. In this manner, the energy contained in the fuel isconverted into the mechanical energy of the rotating shaft, which, forexample, then may be used to rotate the rotor blades of the compressor,such that the supply of compressed air needed for combustion isproduced, and the coils of a generator, such that electrical power isgenerated. During operation, it will be appreciated that componentsexposed to the hot-gas path become highly stressed with extrememechanical and thermal loads. This is due to the extreme temperaturesand velocity of the working fluid, as well as the rotational velocity ofthe turbine. As higher firing temperatures correspond to more efficientheat engines, technology is ever pushing the limits of the materialsused in these applications.

Whether due to extreme temperature, mechanical loading or combination ofboth, component failure remains a significant concern in combustionturbine engines. A majority of failures can be traced to materialfatigue, which typically is forewarned by the onset of crackpropagation. More specifically, the formation of cracks caused bymaterial fatigue remains a primary indicator that a component hasreached the limit of its useful life and may be nearing failure. Theability to detect the formation of cracks remains an important industryobjective, particularly when considering the catastrophic damage thatthe failure of a single component may occasion. Such a failure event maycause a chain reaction that destroys downstream systems and components,which require expensive repairs and lengthy forced outages.

One manner in which the useful life of hot-gas path components may beextended is through the use of protective coatings, such as thermalbarrier coatings. In general, exposed surfaces are covered with thesecoatings, and the coatings insulate the component against the mostextreme temperatures of the hot-gas path. However, as one of ordinaryskill in the art will appreciate, these types of coatings wear orfragment during usage, a process that is typically referred to as“coating spallation” or “spallation”. Spallation may result in theformation and growth of uncoated or exposed areas at discrete areas orpatches on the surface of the affected component. These unprotectedareas experience higher temperatures and, thus, are subject to morerapid deterioration, including the premature formation of fatigue cracksand other defects. In combustion turbine engines, coating spallation isa particular concern for turbine rotor blades and components withincombustor, such as liners and transition piece. Early detection ofcoating spallation may allow an operator to take corrective actionbefore the component becomes completely damaged from the increasedthermal strain or the turbine is forced to shut down.

While the operators of combustion turbine engines want to avoid usingworn-out or compromised components that risk failing during operation,they also have a competing interests of not prematurely replacingcomponents before their useful life is exhausted. That is, operatorswant to exhaust the useful life of each component, thereby minimizingpart costs while also reducing the frequency of engine outages for partreplacements to occur. Accordingly, accurate crack detection and/orcoating spallation in engine components is a significant industry need.However, conventional methods generally require regular visualinspection of parts. While useful, visual inspection is bothtime-consuming and requires the engine be shutdown for a prolongedperiod.

The ability to monitor components in the hot-gas path while the engineoperates for the formation of cracks and the spallation of protectivecoatings remains a longstanding need. What is needed is a system bywhich crack formation and spallation may be monitored while the engineoperates so that necessary action may be taken before a failure eventoccurs or significant component damage is realized. Such a system alsomay extend the life of components as the need for part replacement maybe based on actual, measured wear instead of what is anticipated. Inaddition, such a system would decrease the need or frequency ofperforming evaluations, such as visual inspections, that require engineshutdown. To the extent that these objectives may be achieved in acost-effective manner, efficiency would be enhanced and industry demandwould be high.

BRIEF DESCRIPTION OF THE INVENTION

The present invention, thus, describes a system for detecting defects ina combustion duct of a combustion system of a combustion turbine enginewhile the combustion turbine engine operates, wherein the combustionduct comprises a hot side, which is exposed to combustion gases and,opposing the hot side, a cold side. The system may include: an indicatorcoating disposed on an outer surface of the combustion duct, theindicator coating comprising a detectable substance; and a gas sensorpositioned downstream of the combustor, the gas sensor configured totake a measurement of the amount of the detectable substance in thecombustion products of the combustion turbine engine.

The present invention further includes a method for detecting defects ina combustion duct of a combustion system of a combustion turbine enginewhile the combustion turbine engine operates, wherein the combustionduct comprises a hot side, which is exposed to combustion gases and,opposing the hot side, a cold side. The method may include the steps of:coating a cold side the transition piece with an indicator coating, theindicator coating comprising a detectable substance; positioning a gassensor positioned downstream of the combustor, the gas sensor configuredto take a measurement of the amount of the detectable substance in thecombustion products of the combustion turbine engine; and using the gassensor to determine an amount of the detectable substance in thecombustion products of the combustion turbine engine.

These and other features of the present application will become apparentupon review of the following detailed description of the preferredembodiments when taken in conjunction with the drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more completelyunderstood and appreciated by careful study of the following moredetailed description of exemplary embodiments of the invention taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of an exemplary turbine engine inwhich embodiments of the present application may be used;

FIG. 2 is a sectional view of an exemplary compressor that may be usedin the gas turbine engine of FIG. 1;

FIG. 3 is a sectional view of an exemplary turbine that may be used inthe gas turbine engine of FIG. 1;

FIG. 4 is a sectional view of an exemplary combustor that may be used inthe gas turbine engine of FIG. 1 and in which the present invention maybe employed;

FIG. 5 is a perspective cutaway of an exemplary combustor in whichembodiments of the present invention may be employed;

FIG. 6 illustrates a cross-sectional view of a transition piece and asystem for monitoring material defects according to an exemplaryembodiment of the present invention;

FIG. 7 illustrates the system of FIG. 6 as it may detect a defectaccording to an embodiment of the present invention;

FIG. 8 illustrates cross-sectional view of a transition piece and asystem for monitoring material defects according to an alternativeembodiment of the present invention;

FIG. 9 illustrates the system of FIG. 8 as it may detect a defectaccording to an embodiment of the present invention;

FIG. 10 illustrates cross-sectional view of a transition piece and asystem for monitoring material defects according to an alternativeembodiment of the present invention;

FIG. 11 illustrates a schematic representation of a stack for acombustion turbine engine and a detector according to the embodiment ofFIG. 10; and

FIG. 12 illustrates the system of FIGS. 10 and 11 as it may detect adefect according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, FIG. 1 illustrates a schematicrepresentation of a gas turbine engine 100 in which embodiments of thepresent invention may be employed. In general, gas turbine enginesoperate by extracting energy from a pressurized flow of hot gas that isproduced by the combustion of a fuel in a stream of compressed air. Asillustrated in FIG. 1, gas turbine engine 100 may be configured with anaxial compressor 106 that is mechanically coupled by a common shaft orrotor to a downstream turbine section or turbine 110, and a combustionsystem 112, which, as shown, is a can combustor that is positionedbetween the compressor 106 and the turbine 110.

FIG. 2 illustrates a view of an axial compressor 106 that may be used ingas turbine engine 100. As shown, the compressor 106 may include aplurality of stages. Each stage may include a row of compressor rotorblades 120 followed by a row of compressor stator blades 122. Thus, afirst stage may include a row of compressor rotor blades 120, whichrotate about a central shaft, followed by a row of compressor statorblades 122, which remain stationary during operation. The compressorstator blades 122 generally are circumferentially spaced one from theother and fixed about the axis of rotation. The compressor rotor blades120 are circumferentially spaced about the axis of the rotor and rotateabout the shaft during operation. As one of ordinary skill in the artwill appreciate, the compressor rotor blades 120 are configured suchthat, when spun about the shaft, they impart kinetic energy to the airor working fluid flowing through the compressor 106. As one of ordinaryskill in the art will appreciate, the compressor 106 may have many otherstages beyond the stages that are illustrated in FIG. 2. Each additionalstage may include a plurality of circumferential spaced compressor rotorblades 120 followed by a plurality of circumferentially spacedcompressor stator blades 122.

FIG. 3 illustrates a partial view of an exemplary turbine section orturbine 110 that may be used in a gas turbine engine 100. The turbine110 may include a plurality of stages. Three exemplary stages areillustrated, but more or less stages may be present in the turbine 110.A first stage includes a plurality of turbine buckets or turbine rotorblades 126, which rotate about the shaft during operation, and aplurality of nozzles or turbine stator blades 128, which remainstationary during operation. The turbine stator blades 128 generally arecircumferentially spaced one from the other and fixed about the axis ofrotation. The turbine rotor blades 126 may be mounted on a turbine wheel(not shown) for rotation about the shaft (not shown). A second stage ofthe turbine 110 is also illustrated. The second stage similarly includesa plurality of circumferentially spaced turbine stator blades 128followed by a plurality of circumferentially spaced turbine rotor blades126, which are also mounted on a turbine wheel for rotation. A thirdstage also is illustrated, and similarly includes a plurality ofcircumferentially spaced turbine stator blades 128 and turbine rotorblades 126. It will be appreciated that the turbine stator blades 128and turbine rotor blades 126 lie in the hot gas path of the turbine 110.The direction of flow of the hot gases through the hot gas path isindicated by the arrow. As one of ordinary skill in the art willappreciate, the turbine 110 may have many other stages beyond the stagesthat are illustrated in FIG. 3. Each additional stage may include aplurality of circumferential spaced turbine stator blades 128 followedby a plurality of circumferentially spaced turbine rotor blades 126.

A gas turbine engine of the nature described above may operate asfollows. The rotation of compressor rotor blades 120 within the axialcompressor 106 compresses a flow of air. In the combustor 112, asdescribed in more detail below, energy is released when the compressedair is mixed with a fuel and ignited. The resulting flow of hot gasesfrom the combustor 112 then may be directed over the turbine rotorblades 126, which may induce the rotation of the turbine rotor blades126 about the shaft, thus transforming the energy of the hot flow ofgases into the mechanical energy of the rotating shaft. The mechanicalenergy of the shaft may then be used to drive the rotation of thecompressor rotor blades 120, such that the necessary supply ofcompressed air is produced, and also, for example, a generator toproduce electricity.

Before proceeding further, it will be appreciated that in order tocommunicate clearly the present invention, it will become necessary toselect terminology that refers to and describes certain parts or machinecomponents of a turbine engine and related systems, particularly, thecombustor system. Whenever possible, industry terminology will be usedand employed in a manner consistent with its accepted meaning. However,it is meant that any such terminology be given a broad meaning and notnarrowly construed such that the meaning intended herein and the scopeof the appended claims is unreasonably restricted. Those of ordinaryskill in the art will appreciate that often a particular component maybe referred to using several different terms. In addition, what may bedescribed herein as a single part may include and be referenced inanother context as consisting of several component parts, or, what maybe described herein as including multiple component parts may befashioned into and, in some cases, referred to as a single part. Assuch, in understanding the scope of the invention described herein,attention should not only be paid to the terminology and descriptionprovided, but also to the structure, configuration, function, and/orusage of the component, as provided herein.

In addition, several descriptive terms may be used regularly herein, andit may be helpful to define these terms at this point. These terms andtheir definition given their usage herein is as follows. The term “rotorblade”, without further specificity, is a reference to the rotatingblades of either the compressor or the turbine, which include bothcompressor rotor blades and turbine rotor blades. The term “statorblade”, without further specificity, is a reference the stationaryblades of either the compressor or the turbine, which include bothcompressor stator blades and turbine stator blades. The term “blades”will be used herein to refer to either type of blade. Thus, withoutfurther specificity, the term “blades” is inclusive to all type ofturbine engine blades, including compressor rotor blades, compressorstator blades, turbine rotor blades, and turbine stator blades. Further,as used herein, “downstream” and “upstream” are terms that indicate adirection relative to the flow of a fluid, such as the working fluidthrough the turbine. As such, the term “downstream” refers to adirection that generally corresponds to the direction of the flow ofworking fluid, and the term “upstream” generally refers to the directionthat is opposite of the direction of flow of working fluid. The terms“forward” or “leading” and “aft” or “trailing” generally refer torelative position in relation to the forward end and aft end of theturbine engine (i.e., the compressor is the forward end of the engineand the end having the turbine is the aft end). At times, which will beclear given the description, the terms “leading” and “trailing” mayrefer to the direction of rotation for rotating parts. When this is thecase, the “leading edge” of a rotating part is the edge that leads inthe rotation and the “trailing edge” is the edge that trails.

The term “radial” refers to movement or position perpendicular to anaxis. It is often required to described parts that are at differingradial positions with regard to an axis. In this case, if a firstcomponent resides closer to the axis than a second component, it may bestated herein that the first component is “radially inward” or “inboard”of the second component. If, on the other hand, the first componentresides further from the axis than the second component, it may bestated herein that the first component is “radially outward” or“outboard” of the second component. The term “axial” refers to movementor position parallel to an axis. Finally, the terms “circumferential” or“angular position” refers to movement or position around an axis.

FIGS. 4 and 5 illustrates an exemplary combustor 130 that may be used ina gas turbine engine and in which embodiments of the present inventionmay be used. As one of ordinary skill in the art will appreciate, thecombustor 130 may include a headend 163, which generally includes thevarious manifolds that supply the necessary air and fuel to thecombustor, and an end cover 170. A plurality of fuel lines 137 mayextend through the end cover 170 to fuel nozzles or fuel injectors 138that are positioned at the aft end of a forward case or cap assembly140. It will be appreciated that the cap assembly 140 generally iscylindrical in shape and fixed at a forward end to the end cover 170.

In general, the fuel injectors 138 bring together a mixture of fuel andair for combustion. The fuel, for example, may be natural gas and theair may be compressed air (the flow of which is indicated in FIG. 4 bythe several arrows) supplied from the compressor. As one of ordinaryskill in the art will appreciate, downstream of the fuel injectors 138is a combustion chamber 180 in which the combustion occurs. Thecombustion chamber 180 is generally defined by a liner 146, which isenclosed within a flow sleeve 144. Between the flow sleeve 144 and theliner 146 an annulus is formed. From the liner 146, a transition piece148 transitions the flow from the circular cross section of the liner toan annular cross section as it travels downstream to the turbine section(not shown in FIG. 4). A transition piece impingement sleeve 150(hereinafter “impingement sleeve 150”) may enclose the transition piece148, also creating an annulus between the impingement sleeve 150 and thetransition piece 148. At the downstream end of the transition piece 148,a transition piece aft frame 152 may direct the flow of the workingfluid toward the airfoils that are positioned in the first stage of theturbine 110. It will be appreciated that the flow sleeve 144 and theimpingement sleeve 150 typically has impingement apertures (not shown inFIG. 4) formed therethrough which allow an impinged flow of compressedair from the compressor 106 to enter the cavities formed between theflow sleeve 144 and the liner 146 and between the impingement sleeve 150and the transition piece 148. The flow of compressed air through theimpingement apertures convectively cools the exterior surfaces of theliner 146 and the transition piece 148.

Referring now to FIGS. 6 through 12, several methods for detectingdefects within the transition piece 148 within a combustion turbineengine will be discussed. It will be appreciated that reference to“defects” includes both the formation of cracks within the transitionpiece 148 and the spallation of the protective coating (i.e., thermalbarrier coating) that is typically applied to the interior surface ofthe transition piece.

FIG. 6 illustrates a cross-sectional view of a transition piece 148 anda system for monitoring material defects within the transition piece 148according to an embodiment of the present invention. (It will beappreciated by those of ordinary skill in the art that the systems andmethods described herein may be applied in the same manner to liners 146within the combustion system. The usage of the transition piece 148 inthe several exemplary uses are provided below, accordingly, is meant toapply also to users within the liner 146 of the combustor. When referredto jointly in the appended claims, the transition piece 148 and liner146 will be referred to as a “combustion duct”) FIG. 7 illustrates theoperation of the system as it detects a defect within the transitionpiece 148 according to an exemplary embodiment. It will be appreciatedthat the interior surface of the transition piece 148, which is oftenreferred to as the “hot side”, may be coated with a protective coating161, which may be a conventional thermal barrier coating. According tothe present invention, the exterior surface of the transition piece 148,which is often referred to as the “cold side”, may be coated with anindicator coating 163. In one embodiment, the indicator coating 163, asdescribed in more detail below, may include coating that includes apowder substance, such as zinc, cadmium, magnesium, or any othercolorful powder, and an adhesive. In some embodiments the adhesive mayinclude ceramic adhesives (Resbond™ 919 & 920), ceramic putties, orepoxy silicones, which have good creep resistance properties at hightemperatures, or other similar types of materials or adhesives. Asshown, the indicator coating 163 may be applied to large areas of thecold side of the transition piece 148. It will be appreciated that theadhesive will bind the coating to the cold side of transition piece 148.

According to embodiments of the present invention, a detector 165 may bepositioned such that it detects light that is either reflected oremanating from the cold side of the transition piece 148, as illustratedin FIG. 6. The detector 165 may be connected to stationary structure 166such that its position and ability to monitor the cold side of thetransition piece 148 remains stable. The detector 165 may be positionsuch that a particular area of the transition piece 148 is within thedetector's 148 field of view. In some embodiments, the stationarystructure 166 may include a section of the combustor casing. In otherembodiments, the stationary structure 166 may include a section of theimpingement sleeve 150 that surrounds the transition piece 148. Thedetector 165 may be positioned a predetermined distance from transitionpiece 148 such that a desirable coverage area is achieved.

In one embodiment, the detector 165 comprises a conventional photosensoror photodetector, i.e., a conventional sensor that is able to detectlight. More specifically, the detector may comprises any conventionalphotodetector that is capable of detecting the changes to the indicatorcoating 163 that are described herein. According to one embodiment, thedetector 165 comprises a conventional color sensor, which may include aBayer type sensor, a Foveon X3 type sensor, a 3CCD type sensor or othertype of color sensor. According to an alternative embodiment, thedetector 165 comprises a photodiode light sensor or other type ofphotodetector configured to detect bright light or light flashes thatmay occur upon the combustion of substances that may be used to dope theindicator coating 163.

As illustrated in FIG. 6, the detector 165 may be in communication witha control unit 170 that is configured to determine whether color orlight has been detected by the detector 165 that exceeds predeterminedcriteria. In the event that the predetermined criteria has been crossed,the control unit 170 may then be configured to send an automatic warningsignal or perform a corrective action. For example, the warning signalmay comprise an alarm or other communication, such as an e-mail orautomated message, to an operator, and the corrective action may includeshutting down the combustion turbine engine.

In operation, the adhesive of the indicator coating 163 binds the powderof the coating to the cold side of the transition piece 148. Absent theformation of a defect 173, it will be appreciated that the indicatorcoating 163 may be configured such that it remains bound to the coldside of the transition piece 148 and, accordingly, the detector 165registers no change in the light reflected or admitted therefrom.

As illustrated in FIG. 7, a defect 173 may form within the transitionpiece 148. As stated, the defect 173 may include a crack within thetransition piece 148 that causes the spallation of protective coating161, or the defect 173 may include erosion or spallation of protectivecoating 161 from the transition piece 148. With the formation of thedefect 173, the temperature of the transition piece 148 will increaseand result in a “hotspot” forming along a section of the cold side ofthe transition piece 148. In the case of a defect 173 that includes acrack through the transition piece 148, this may include hot gases beingingested through the crack, which may cause an even greater increase intemperature along the cold side of the transition piece 148.

Given the increase in temperature, according to an embodiment of thepresent invention, it will be appreciated that the coating may beconfigured such that the adhesive begins to lose its adhesivecharacteristics and/or the powder substance begins melting. As one ofordinary skill in the art will appreciate, these conditions may causethe cold side of the transition piece 148 to lose its coverage of theindicator coating 163, i.e., develop bare patches as illustrated in FIG.7. In the case where the detector 165 comprises a color sensor, thiswill cause a change in color that may be detected by the detector 165.For example, the color of the cold side of the transition piece 148 maychange due to thermal distress. Or, for example, the color of the coldside of the transition piece 148 may be gray, while the indicatorcoating was white, such that the removal of the indicator coating 163causes a distinct color change. As stated, in exemplary embodiments, thedetection of the change in color may cause the control unit 170 toprovide a warning notification that a defect 173 is likely and/or thatcorrective action should be taken. It will be appreciated that thesensitivity of the system may be adjusted by using different criteriaconcerning the signal received from the detector before a warningnotification is issued.

In an alternative embodiment, the indicator coating 163 may include amaterial, such as magnesium, that admits bright light and/or brightflashes upon being subject to the high temperatures of ingested hot pathgases. In another manner, this event could also be detected, after thecoating spalls (due to material melting or loss of adhesion property)and flows along the cold side of the transition piece 148 to the airinlet (not shown) of the combustor or through the leakage path betweentransition piece and liner (hula seal path) or through a crack. Theloose pieces 163 a may combust and thereby release the detectable brightlight at the hot side of transition piece/liner which could be detectedby a spectroscope installed either at transition piece aft end or atstack (similarly to the system illustrated in FIGS. 10 through 12). Inthis case, the detector 165 may include a photodetector or spectroscopethat is capable of registering such bright light and/or bright flashes.For example, the detector 165 may include a photodiode. In this case,the raised temperatures and/or ingested gases that may occur upon theformation of a defect 173 may cause the magnesium or other such materialto produce the bright light or bright flashes. In exemplary embodiments,the detection of the bright light/flashes may cause the control unit 170to provide a warning notification that a defect 173 is likely and/orthat corrective action should be taken. It will be appreciated that thesensitivity of the system may be adjusted by using different criteriaconcerning the signal received from the detector 165 before a warningnotification is issued.

In another alternative embodiment, the two prior embodiments may form acombined embodiment that detects both color change and brightlights/flashes. It will be appreciated that in such an embodiment thedifferent modes of detection may be configured to communicate varyingcategories of defects 173. For example, the detection of a color changeby the detector 165 may indicate a hotspot resulting from the erosion ofprotective coating 161 from the inner surface of the transition piece148. The detection of the bright light/flashes, on the other hand, mayindicate a more serious problem that includes the ingestion of hot flowpath gases through a crack in the transition piece 148. In any case, theparameters, of course, may be adjusted depending on the characteristicsof the system and the desired sensitivity, as one of ordinary skill inthe art will appreciate.

FIG. 8 illustrates a cross-sectional view of a transition piece and asystem for monitoring material defects according to the presentinvention, while FIG. 9 illustrates the operation of the system as itdetects a defect according to an exemplary embodiment.

Similar to the embodiments discussed above, the interior surface of thetransition piece may be coated with a protective coating 161, which maybe a conventional thermal barrier coating. The exterior surface of thetransition piece 148, may be coated with an indicator coating 163. Inthis embodiment, the indicator coating 163 may be any conventionalcoating that fulfills the performance criteria described herein. Forexample, the indicator coating 163, in some preferred embodiments, mayinclude ceramic adhesives, ceramic putties, or epoxy silicones, whichhave good creep resistance properties at high temperatures, or othersimilar types of materials or adhesives. As shown, the indicator coating163 may be applied to large areas of the cold side of the transitionpiece 148. It will be appreciated that the adhesive qualities of thecoating will bind the indicator coating to the cold side of transitionpiece 148. In preferred embodiments, the indicator coating 161 may beapplied such that it has a thickness of approximately 0.001 to 0.80inches.

According to alternative embodiments of the present invention, aproximity sensor 175 may be connected to stationary structure 166 suchthat its position in relation to the transition piece 148 is fixed. Theproximity sensor 175 may be position such that a particular area of thetransition piece 148 is within the field of view of the proximity sensor175. In some embodiments, the stationary structure 166 may include asection of the combustor casing. In other embodiments, the stationarystructure 166 may include a section of the impingement sleeve 150 thatsurrounds the transition piece 148. The detector 165 may be positioned asuitable distance from transition piece 148 according to the performancecharacteristics of the particular proximity sensor 175. In one preferredembodiment, the proximity sensor 120 is a laser proximity probe. Inother embodiments, the proximity sensor 120 may be an eddy currentsensor, capacitive sensor, microwave sensor, or any other similar typeof device.

As illustrated in FIG. 8, the proximity sensor 175 may be incommunication with a control unit 170 that is configured to determinewhether a change in the distance between the proximity sensor and theindicator coating 163 has been detected by the proximity sensor 175 thatexceeds predetermined criteria. In the event that the predeterminedcriteria has been exceeded, the control unit 170 may then be configuredto send an automatic warning signal or perform a corrective action. Forexample, the warning signal may comprise an alarm or othercommunication, such as an e-mail or automated message, to an operator,and the corrective action may include shutting down the combustionturbine engine.

In operation, the adhesive of the indicator coating 163 generally bindsthe coating to the cold side of the transition piece 148. Absent theformation of a defect 173, it will be appreciated that the indicatorcoating 163 may be configured such that it remains bound to the coldside of the transition piece 148 and, accordingly, the proximity sensor175 registers no change in the distance (which is indicated as “d1” inFIG. 8) to the surface of the indicator coating 163.

As illustrated in FIG. 9, a defect 173 may form within the transitionpiece 148. As stated, the defect 173 may include a crack within thetransition piece 148 that causes the spallation of protective coating161, or the defect 173 may include erosion or spallation of protectivecoating 161 from the transition piece 148 that forms in the absence of acrack within the transition piece 148. With the formation of the defect173, the temperature of the transition piece 148 will increase andresult in a “hotspot” forming along a section of the cold side of thetransition piece 148. In the case of a defect 173 that includes a crackthrough the transition piece 148, this may include hot gases beingingested through the crack, which may cause an even greater increase intemperature along the cold side of the transition piece 148.

Given the increase in temperature, according to an embodiment of thepresent invention, it will be appreciated that the coating may beconfigured such that the adhesive begins to lose its adhesivecharacteristics and/or the powder substance begins melting. As one ofordinary skill in the art will appreciate, these conditions may causethe cold side of the transition piece 148 to lose its coverage of theindicator coating 163, i.e., develop bare patches as illustrated in FIG.7. The proximity sensor 175 may measure a change in the distance to thetransition piece 148 (i.e., the proximity sensor 175 may indicate thedistance has increased to the distance indicated as “d2” in FIG. 9). Inexemplary embodiments, the detection of the change in distance may causethe control unit 170 to provide a warning notification that a defect 173is likely and/or that corrective action should be taken. It will beappreciated that the sensitivity of the system may be adjusted by usingdifferent criteria concerning the change in distance required before awarning notification is issued.

FIGS. 10 and 11 illustrate a view of a transition piece and downstreamstack, respectively, that include a system for monitoring materialdefects according to the present invention, while FIG. 12 illustratesthe operation of the system as it detects a defect according to anexemplary embodiment.

Similar to the embodiments discussed above, the interior surface of thetransition piece may be coated with a protective coating 161, which maybe a conventional thermal barrier coating. The exterior surface of thetransition piece 148, may be coated with an indicator coating 163. Inthis embodiment, the indicator coating 163, as described in more detailbelow, may be ceramic adhesives, ceramic putties, or epoxy silicones,which have good creep resistance properties at high temperatures, orother similar types of materials or adhesives. As described in moredetail below, the indicator coating 163 may include a substance which isdetectable by a gas analyzer or sensor 181 located downstream. Incertain preferred embodiments, this detectable substance is a rare earthelement. In other embodiments, the detectable substance may be cadmiumor magnesium. It will be appreciated that other substances may also beused. As shown, the indicator coating 163 may be applied to large areasof the cold side of the transition piece 148. It will be appreciatedthat the adhesive qualities of the coating will bind the indicatorcoating to the cold side of transition piece 148.

According to alternative embodiments of the present invention, asstated, a gas analyzer 181 may be located in a suitable locationdownstream of the combustor. Once such preferred locations is within thestack 178 of the combustion turbine engine, as illustrated in FIG. 11.The gas sensor 181 may include any conventional gas analyzer suitablefor the described application, as one of ordinary skill may or willappreciate. In a preferred embodiment, the gas sensor 181 comprises achromatography analyzer. Other types of conventional gas sensors mayalso be used.

As illustrated in FIG. 11, the gas sensor 181 may be in communicationwith a control unit 170 that is configured to determine whether the gasbeing analyzed includes the detectable substance of the indicatorcoating 163. The control unit 170 may be configured to determine whethera predetermined threshold of the detectable substance has been exceeded.In the event that the predetermined threshold has been exceeded, thecontrol unit 170 may then be configured to send an automatic warningsignal or perform a corrective action. For example, the warning signalmay comprise an alarm or other communication, such as an e-mail orautomated message, to an operator, and the corrective action may includeshutting down the combustion turbine engine.

In operation, the adhesive of the indicator coating 163 generally bindsthe coating to the cold side of the transition piece 148. Absent theformation of a defect 173, it will be appreciated that the indicatorcoating 163 may be configured such that it remains bound to the coldside of the transition piece 148 and, accordingly, the gas sensorregisters no detection of the detectable substance of indicator coating161 within the combustion products flowing through the stack 170.

As illustrated in FIG. 9, a defect 173 may form within the transitionpiece 148. As stated, the defect 173 may include a crack within thetransition piece 148 that causes the spallation of protective coating161, or the defect 173 may include erosion or spallation of protectivecoating 161 from the transition piece 148 that forms in the absence of acrack within the transition piece 148. With the formation of the defect173, the temperature of the transition piece 148 will increase andresult in a “hotspot” forming along a section of the cold side of thetransition piece 148. In the case of a defect 173 that includes a crackthrough the transition piece 148, this may include hot gases beingingested through the crack, which may cause an even greater increase intemperature along the cold side of the transition piece 148.

Given the increase in temperature, according to an embodiment of thepresent invention, it will be appreciated that the coating may beconfigured such that the adhesive begins to lose its adhesivecharacteristics and/or the powder substance begins melting. As one ofordinary skill in the art will appreciate, these conditions may causethe indicator coating 163 to erode from cold side of the transitionpiece 148. Pieces of the eroded indicator coating (which are indicatedas “163 a” in FIG. 12) may flow along the cold side of the transitionpiece 148 to the air inlet (not shown) of the combustor. The loosepieces 163 a may combust and thereby release the detectable substancewithin the indicator coating 161. Alternatively, the detectablesubstance may be released upon the development of a hotspot and/oringested into the hot gas flow path through a crack formed through thetransition piece 148.

The gas sensor 181, which, as stated, is located downstream of thecombustor, and, in one preferred embodiment, within the stack 178, thenmay detect the detectable substance of the indicator coating 163. Inexemplary embodiments, the detection of the detectable substance maycause the control unit 170 to provide a warning notification that adefect 173 is likely and/or that corrective action should be taken. Itwill be appreciated that the sensitivity of the system may be adjustedby requiring different threshold levels of the substance be detectedbefore a corrective action is taken. In this manner, the catastrophicfailure of transition piece may be avoided.

Alternatively, according to another embodiment of the present invention,the protective coating 161 (for example, the thermal barrier coating) onhot side of transition piece 148 could be doped with the detectablesubstance. The gas sensor 181 at the stack 178 or other downstreamlocation then may detect the traces of the detectable substance as theprotective coating 161 spalls. This will be indicative of protectivecoating spallation and/or crack formation.

It will be appreciated that by monitoring crack formation and coatingspallation while the engine operates may reduce the need for regularvisual inspections, which may also reduce engine down time. As will beappreciated, typically the transition piece is not inspected until thecombustion system undergoes a diagnostic check after several thousandsof hours of operation. Monitoring for crack formation and spallationwhile the engine operates may detect the formation of a significantdefect that otherwise would have gone unnoticed until this inspectionoccurs. Depending on the severity of the defect, significant damage mayoccur if the engine continues to operate and corrective action is nottaken, particularly if a failure liberates pieces of the transitionpiece that cause damage to downstream components. Such an event may beavoided if the real-time monitoring capabilities of the presentinvention are available.

As one of ordinary skill in the art will appreciate, the many varyingfeatures and configurations described above in relation to the severalexemplary embodiments may be further selectively applied to form theother possible embodiments of the present invention. For the sake ofbrevity and taking into account the abilities of one of ordinary skillin the art, all of the possible iterations is not provided or discussedin detail, though all combinations and possible embodiments embraced bythe several claims below or otherwise are intended to be part of theinstant application. In addition, from the above description of severalexemplary embodiments of the invention, those skilled in the art willperceive improvements, changes and modifications. Such improvements,changes and modifications within the skill of the art are also intendedto be covered by the appended claims. Further, it should be apparentthat the foregoing relates only to the described embodiments of thepresent application and that numerous changes and modifications may bemade herein without departing from the spirit and scope of theapplication as defined by the following claims and the equivalentsthereof.

1. A system for detecting defects in a combustion duct of a combustionsystem of a combustion turbine engine while the combustion turbineengine operates, wherein the combustion duct comprises a hot side, whichis exposed to combustion gases and, opposing the hot side, a cold side,the system comprising: an indicator coating disposed on an outer surfaceof the combustion duct, the indicator coating comprising a detectablesubstance; and a gas sensor positioned downstream of the combustor, thegas sensor configured to take a measurement of the amount of thedetectable substance in the combustion products of the combustionturbine engine.
 2. The system according to claim 1, wherein theindicator coating comprises a coating that degrades above a thresholdtemperature.
 3. The system according to claim 2, wherein the indicatorcoating is configured such that the degradation above the thresholdtemperature causes the indicator coating to detach from the cold side ofthe combustion duct.
 4. The system according to claim 2, wherein theindicator coating comprises an adhesive; wherein the adhesive of theindicator coating is configured to bind to the cold side of thecombustion duct until a threshold temperature is achieved; and whereinthe adhesive characteristics of the adhesive of the indicator coating isconfigured to degrade once the threshold temperature is achieved.
 5. Thesystem according to claim 4, wherein the indicator coating is configuredsuch that degradation above the threshold temperature causes the coatingto detach from the cold side of the combustion duct.
 6. The systemaccording to claim 3, wherein the hot side comprises a protectivecoating; and wherein the threshold temperature corresponds to anelevated temperature that results from a defect in the protectivecoating of the hot side.
 7. The system according to claim 6, wherein thedefect comprises spallation of the protective coating from an area onthe hot side, the area of spallation comprising at least a thresholdsize, wherein the threshold size corresponds to the size required tocause the threshold temperature at the cold side.
 8. The systemaccording to claim 3, further comprising a control unit thatcommunicates with the gas sensor; wherein the control unit and gassensor are configured to take and record an initial measurement of theamount of the detectable substance in the combustion products of thecombustion turbine engine; and wherein the control unit and gas sensorare configured to take and record an subsequent measurement of theamount of the detectable substance in the combustion products of thecombustion turbine engine.
 9. The system according to claim 8, whereinthe control unit is configured to compare the initial measurementagainst the subsequent measurement to determine if the amount of thedetectable substance in the combustion products has increased.
 10. Thesystem according to claim 9, wherein the control unit is configured todetermine if the amount of the detectable substance in the combustionproducts has increased beyond a predetermined threshold; and wherein thecontrol unit is configured to send a warning communication if the amountof the detectable substance in the combustion products has increasedbeyond the predetermined threshold.
 11. The system according to claim 6,wherein the combustion duct comprises one of a transition piece and aliner; wherein the protective coating comprises a thermal barriercoating; and wherein the adhesive of the indicator coating comprises oneof a ceramic adhesive, a ceramic putty, and an epoxy silicone.
 12. Thesystem according to claim 2, wherein the gas sensor is disposed in astack.
 13. The system according to claim 2, wherein the detectablesubstance comprises a rare earth element.
 14. The system according toclaim 2, wherein the detectable substance comprises cadmium ormagnesium.
 15. The system according to claim 2, wherein the gas sensorcomprises a chromatography analyzer.
 16. A method for detecting defectsin a combustion duct of a combustion system of a combustion turbineengine while the combustion turbine engine operates, wherein thecombustion duct comprises a hot side, which is exposed to combustiongases and, opposing the hot side, a cold side, the method including thesteps of: coating a cold side the transition piece with an indicatorcoating, the indicator coating comprising a detectable substance;positioning a gas sensor positioned downstream of the combustor, the gassensor configured to take a measurement of the amount of the detectablesubstance in the combustion products of the combustion turbine engine;and using the gas sensor to determine an amount of the detectablesubstance in the combustion products of the combustion turbine engine.17. The method according to claim 16, wherein the indicator coatingcomprises a coating that degrades above a threshold temperature; andwherein the indicator coating is configured such that the degradationabove the threshold temperature causes the indicator coating to detachfrom the cold side of the combustion duct and the detectable substanceto enter the combustion products of the combustion turbine engine;further comprising the step of determining if the an amount of thedetectable substance in the combustion products of the combustionturbine engine exceeds a predetermined threshold.
 18. The methodaccording to claim 17, wherein the indicator coating comprises anadhesive; wherein the adhesive of the indicator coating is configured tobind to the cold side of the combustion duct until a thresholdtemperature is achieved; and wherein the adhesive characteristics of theadhesive of the indicator coating is configured to degrade once thethreshold temperature is achieved.
 19. The method according to claim 17,wherein the hot side comprises a protective coating; and wherein thethreshold temperature corresponds to an elevated temperature thatresults from a defect in the protective coating of the hot side.
 20. Themethod according to claim 19, wherein the defect comprises spallation ofthe protective coating from an area on the hot side, the area ofspallation comprising at least a threshold size, wherein the thresholdsize corresponds to the size required to cause the threshold temperatureat the cold side.
 21. The method according to claim 17, furthercomprising the steps of: taking and recording an initial measurement ofthe amount of the detectable substance in the combustion products of thecombustion turbine engine; taking and recording a subsequent measurementof the amount of the detectable substance in the combustion products ofthe combustion turbine engine; and comparing the initial measurementagainst the subsequent measurement to determine if the amount of thedetectable substance in the combustion products has increased, and, ifthe amount of the detectable substance in the combustion products hasincreased, the rate of the increase.
 22. The method according to claim21, wherein the control unit is configured to determine if the rate ofincrease is greater than a predetermined threshold.
 23. The methodaccording to claim 19, wherein the combustion duct comprises one of atransition piece and a liner; wherein the protective coating comprises athermal barrier coating; and wherein the adhesive of the indicatorcoating comprises one of a ceramic adhesive, a ceramic putty, and anepoxy silicone.
 24. The method according to claim 23, wherein the gassensor is disposed in a stack; and wherein the detectable substancecomprises a rare earth element.
 25. The method according to claim 24,wherein the detectable substance comprises cadmium or magnesium; andwherein the gas sensor comprises a chromatography analyzer.